The present invention relates to the general field of turboprops provided with two contrarotating propellers driven in rotation by means of a single turbine.
The invention relates more particularly to feeding fluid to a hydraulic actuator for controlling the pitch of the fan blades of a two-propeller turboprop.
In known manner, an airplane turboprop with two propellers has two contrarotating sets of unducted fan blades that are adjustable in pitch. In certain two-propeller turboprop configurations, these sets of fan blades are driven in rotation by a power turbine having two contrarotating rotors. In other configurations more particularly concerned by the present invention, the sets of fan blades are driven by a single rotor of the power turbine via an epicyclic gear train forming a stepdown contrarotating gearbox. By way of example, reference may be made to document FR 2 942 203, which describes an embodiment of such a configuration.
The contrarotating propellers of such a turboprop may be driven in rotation directly or indirectly via the epicyclic gear train. In general, the epicyclic gear train has an inlet that is connected upstream to a rotor shaft of the power turbine in order to be driven thereby, and two outlets, each of which is connected downstream to a respective power shaft for driving rotation of a respective one of the two sets of turboprop fan blades in contrarotating manner.
Furthermore, the angle of orientation of the fan blades in each set (generally referred to as its “pitch”) constitutes one of the parameters that enables the thrust from the turboprop and the speed of rotation of the propellers to be controlled. One known technique for controlling the pitch of the fan blades in flight is to make use, for each set of fan blades, of a synchronization ring coupled to each of the blades in the set. A hydraulic actuator positioned at the center of the turboprop and constrained to rotate with the turbine rotor is used for turning the synchronization ring about the longitudinal axis of the turboprop (via a linkage of connecting rods), thereby enabling all of the blades in a given set to be positioned at the same angle. By way of example, reference may be made to patent application FR 11/56443 filed by the Applicant on Jul. 13, 2011 (and not yet published), which describes an embodiment of such a mechanism.
With that type of mechanism, there arises a problem of feeding fluid to the chambers of the actuators. In particular, the admission of fluid takes place via tubes that are fastened to the stationary portions of the turboprop, while the actuators, and thus their chambers, are rotating since they are driven in rotation by the turbine rotor. It is therefore necessary to cause the fluid to pass from a stationary frame of reference to a rotary frame of reference. Furthermore, the transfer of fluid from fluid-admission tubes to the chambers of the control actuators must take place in as small a space as possible in order to avoid increasing the length of the engine.